Parker Anna L, Benkman Craig W
Department of Zoology and Physiology University of Wyoming Laramie Wyoming USA.
Department of Biology University of North Carolina Chapel Hill North Carolina USA.
Ecol Evol. 2020 May 9;10(12):6001-6008. doi: 10.1002/ece3.6339. eCollection 2020 Jun.
Serotiny, the retention of seeds in a canopy seed bank until high temperatures cause seeds to be released, is an important life history trait for many woody plants in fire-prone habitats. Serotiny provides a competitive advantage after fire but increases vulnerability to predispersal seed predation, due to the seeds being retained in clusters in predictable locations for extended periods. This creates opposing selection pressures. Serotiny is favored in areas of high fire frequency, but is selected against by predispersal seed predators. However, predation also selects for cone traits associated with seed defense that could reduce predation on serotinous cones and thereby relax selection against serotiny. This helps explain the elevated defenses in highly serotinous species. However, whether such interactions drive variation in seed defenses within variably serotinous populations has been studied rarely. We investigated the effects of phenotypic selection exerted by red squirrel () predation on Rocky Mountain lodgepole pine () seeds. Squirrels preferentially harvested cones with more and larger seeds, indicating a preference for a higher food reward. We found evidence for stronger selection on trees with serotinous cones, which presumably accounts for the elevated defenses of and lower predation on serotinous compared to non-serotinous cones. Lower levels of predation on serotinous cones in turn lessen selection against serotiny by squirrels. This has important implications because the frequency of serotiny in lodgepole pine has profound consequences for post-fire communities and ecosystems widespread in the Rocky Mountains.
种子迟落现象，即种子在树冠种子库中留存，直至高温促使种子释放，是许多生长在易发生火灾栖息地的木本植物的一项重要生活史特征。种子迟落在火灾后提供了竞争优势，但由于种子长时间成簇留存于可预测的位置，增加了种子在扩散前遭受捕食的脆弱性。这产生了相互对立的选择压力。在火灾频发地区，种子迟落受到青睐，但会受到扩散前种子捕食者的不利选择。然而，捕食也会选择与种子防御相关的球果特征，这可能会减少对具迟落性球果的捕食，从而减轻对种子迟落现象的不利选择。这有助于解释具高度迟落性的物种中增强的防御机制。然而，这种相互作用是否驱动了具不同程度迟落性种群内种子防御的变异，此前鲜有研究。我们调查了红松鼠（）捕食对落基山黑松（）种子施加的表型选择的影响。松鼠优先采集种子更多、更大的球果，表明它们偏好更高的食物回报。我们发现证据表明，对具迟落性球果的树木存在更强的选择作用，这大概解释了具迟落性球果相对于非迟落性球果而言，防御增强且捕食减少的现象。具迟落性球果较低的捕食水平反过来又减轻了松鼠对种子迟落现象的不利选择。这具有重要意义，因为落基山黑松中种子迟落的频率对落基山脉广泛分布的火灾后群落和生态系统有着深远影响。
